I kind of feel like not paying is better than offering a pitifully low sum. Lots of comics start out with a few friends working together on a story they're passionate about. If the premise is truly interesting, it can be a lot of fun writing with another person, and though some posters may truly just be asking for a free subordinate, I do think there are some who are just looking to do something fun with a new friend.
Meanwhile, asking for a low sum doesn't give the opportunity for that same kind of relationship and is just plain disrespectful.
This might be a weird analogy, but it's kinda like sex:
Having sex with someone for free is fun and people do it all the time. Having sex with someone for $400 is fine too. But offering someone $10 for sex is insulting.